M48T37Y-70MH1E STMicroelectronics, M48T37Y-70MH1E Datasheet - Page 15

• Manufacturer Part Number: M48T37Y-70MH1E
• Description: IC TIMEKPR NVRAM 256KBIT5V 44SOH
• Manufacturer: STMicroelectronics
• Series: Timekeeper®r
• Type: Clock/Calendar/NVSRAMr

Specifications of M48T37Y-70MH1E

• Memory Size: 256K (32K x 8)
• Time Format: HH:MM:SS (24 hr)
• Date Format: YY-MM-DD-dd
• Interface: Parallel
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 44-SOH
• Bus Type: Parallel
• User Ram: 32KB
• Operating Supply Voltage (typ): 5V
• Package Type: SOH
• Operating Supply Voltage (max): 5.5V
• Operating Supply Voltage (min): 4.5V
• Operating Temperature Classification: Commercial
• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Pin Count: 44
• Mounting: Surface Mount
• Memory Configuration: 32K X 8
• Nvram Features: RTC
• Interface Type: Parallel
• Access Time: 70ns
• Supply Voltage Range: 4.5V To 5.5V
• Memory Case Style: SOIC
• No. Of Pins: 44
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-2854-5; M48T37Y-70MH1

Figure 9. Back-up Mode Alarm Waveforms
Calibrating the Clock
The M48T37Y/V is driven by a quartz controlled
oscillator with a nominal frequency of 32,768 Hz.
The devices are tested not to exceed ±35 PPM
(parts per million) oscillator frequency error at
25 °C, which equates to about ±1.53 minutes per
month. With the calibration bits properly set, the
accuracy of each M48T37Y/V improves to better
than +1/–2 PPM at 25 °C.
The oscillation rate of any crystal changes with
temperature (see
chips compensate for crystal frequency and tem-
perature shift error with cumbersome trim capaci-
tors. The M48T37Y/V design, however, employs
periodic counter correction. The calibration circuit
adds or subtracts counts from the oscillator divider
circuit at the divide by 256 stage, as shown in
ure 12., page
blanked (subtracted, negative calibration) or split
(added, positive calibration) depends upon the
value loaded into the five-bit Calibration byte found
in the Control Register. Adding counts speeds the
clock up, subtracting counts slows the clock down.
The Calibration Byte occupies the five lower order
bits (D4-D0) in the Control Register 7FF8h. These
bits can be set to represent any value between 0
and 31 in binary form. Bit D5 is the Sign Bit; '1' in-
dicates positive calibration, '0' indicates negative
calibration. Calibration occurs within a 64 minute
cycle. The first 62 minutes in the cycle may, once
V CC
V PFD (max)
V PFD (min)
V SO
ABE, AFE bit in Interrupt Register
AF bit in Flags Register
IRQ/FT
19. The number of times pulses are
Figure 11., page
HIGH-Z
19). Most clock
Fig-
per minute, have one second either shortened by
128 or lengthened by 256 oscillator cycles. If a bi-
nary '1' is loaded into the register, only the first 2
minutes in the 64 minute cycle will be modified; if
a binary 6 is loaded, the first 12 will be affected,
and so on.
Therefore, each calibration step has the effect of
adding 512 or subtracting 256 oscillator cycles for
every 125, 829, 120 (64 minutes x 60 seconds/
minute x 32,768 cycles/second) actual oscillator
cycles, that is +4.068 or –2.034 PPM of adjust-
ment per calibration step in the calibration register.
Assuming that the oscillator is in fact running at ex-
actly 32,768 Hz, each of the 31 increments in the
Calibration Byte would represent +10.7 or –5.35
seconds per month which corresponds to a total
range of +5.5 or –2.75 minutes per month.
Two methods are available for ascertaining how
much calibration a given M48T37Y/V may require.
The first involves simply setting the clock, letting it
run for a month and comparing it to a known accu-
rate reference (like WWW broadcasts). While that
may seem crude, it allows the designer to give the
end user the ability to calibrate his clock as his en-
vironment may require, even after the final product
is packaged in a non-user serviceable enclosure.
All the designer has to do is provide a simple utility
that accesses the Calibration Byte.
tREC
M48T37Y, M48T37V
HIGH-Z
AI03254B
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